In a recent Musotalk vIdeo with Holger Steinbrink (whom many may know is one of the actual Beta testers and prime Cubase tutorial authors), at about 2 minutes in he dispells the idea that the audio engine has been totally revamped and describes that in fact the audio engine has simply been improved upon in regards to Asio guard in order to improve processor performance by the real-time monitoring and handling of time critical and nocritcal processing.
Steinberg Cubase Pro 8 im Überblick - Lohnt sich das Update? - YouTube (unfortunately only in german).